The invention relates generally to the field of molding of plastic articles and, more particularly, to a method and apparatus for trimming molded plastic articles.
Procedures for blow molding double wall plastic articles typically involve the formation of flash or excess material around the perimeter of the part being formed. This flash is pressed thin, or "pinched off" by means of metal to metal contact areas of the opposing mold halves, at the mold parting line and adjacent to the mold cavity or cavities. This pinchoff area is typically relatively wide, on the order of 0.025 to 0.050 inches. When the flash is torn or cut from the molded part, a significant amount of the pinched flash remains attached to said part and must be subsequently removed by mechanical trimming.
In response to the pinchoff problem, a mold construction was developed which is known as "zero land" construction whereby the amount of flash is greatly reduced. However, when the flash is removed from the part, the remaining parting line edge is sharp. This sharp edge is unacceptable in some instances. For example, plastic cases manufactured to hold children's toys cannot have sharp edges due to the risk of injury to children.
In both of the above processes, pinchoff and sharp edges have traditionally been removed by hand with a knife. This hand trimming causes several problems, such as the direct increase in labor cost, inconsistent trimming quality and the possibility of repetitive motion syndrome in the wrists of the hand trimmers.
Another approach has been to heat trim the edges of "zero land" molded articles with a hand held propane torch. This method produces acceptably rounded edges of the articles but still involved the above-described problems associated with hand trimming.
It is therefore desirable to trim blow molded plastic articles in a procedure which does not involve substantial additional labor costs, which produces consistent quality trimming, and which does not pose the risk of injury to operators.
U.S. Pat. Nos. 5,273,422 and 5,431,865 assigned to the assignee of the present application provide an excellent alternative for addressing the foregoing problems in the industry. However, each of these patents, as well as the use of a hand torch, involve the use of a torch for impinging a flame on the workpiece, and therefore require a source of fuel such as propane and the like for the torch. Keeping and using such fuel, however, leads to apprehension in personnel as well as additional precautions which must be taken to ensure safe storage, handling and use of highly combustible materials.
It is therefore the primary object of the present invention to provide an apparatus for trimming blow molded plastic articles which does not involve the use of flame and highly combustible fuel materials.
It is a further object of the present invention to provide an apparatus for trimming plastic articles which produces consistent quality trimming of sharp edges of plastic molded articles.
It is still a further object of the present invention to provide an apparatus for trimming molded plastic articles which does not involve repetitive hand motions of operators and which, therefore, does not pose the risk of repetitive motion syndrome.
It is another object of the present invention to provide an apparatus for trimming which protects hinge portions and other areas of the article during trimming.
Other objects and advantages will become apparent to those skilled in the art upon a consideration of the following disclosure of the invention.